Restaurants and cafes should take steps to warn diners about possible allergens in food, a watchdog has said.

The Food Standards Agency (FSA) said products made with ingredients that may cause an allergic reaction should have them listed on a card, label or menu.

Its new voluntary guidelines are backed by an advice booklet which warns that "eating even a small bit of food" can cause illness or death.

Allergic reactions can be caused by nuts, milk, soya, shellfish or eggs.

Mustard, gluten and celery can also have an adverse effect when consumed.

The advice booklet says: "When someone has a food allergy, eating even a small bit of that food can make them very ill. Sometimes they could even die."

It is essential that cafes, delis and restaurants are fully aware of these guidelines

Sarah Sleet Coeliac UK

The FSA said staff should always check whether a products contains a potential allergen when asked by a customer.

And up-to-date lists of ingredients for ready-made foods, such as sandwich fillings, should also be kept to hand.

The introduction of new guidelines follows evidence that food allergies are becoming more common.

Under the current approach, firms which sell food prepared or wrapped on their own premises are not legally required to say whether their products contain potential allergens.

'Safe choice'

This is the case in restaurants, cafes, bakeries, delicatessen counters and salad bars.

Booklets and posters have been created to promote the guidelines to catering businesses and staff.

Coeliac UK, which represents people with gluten allergies, has welcomed the new guidance.

Sarah Sleet, its chief executive, said: "It is essential that cafes, delis and restaurants are fully aware of these guidelines and have a strategy for dealing with allergens be it from chefs to serving staff to ensure people with coeliac disease can make a safe choice."